Method for managing packets for v2x communication and apparatus therefor

ABSTRACT

A method for discarding at least one packet by a user equipment (UE) in a wireless communication system is disclosed. The method includes steps of storing the at least one packet received from an upper layer in a buffer; determining whether or not a number of packets in the buffer is equal to or greater than a threshold value; and discarding the at least one packet from the buffer when the number of packets in the buffer is equal to or greater than the threshold value.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for managing packets for a V2X(Vehicle-to-Everything) communication and an apparatus therefor.

BACKGROUND ART

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, referred to as LTE) communication system isdescribed in brief.

FIG. 1 is a view schematically illustrating a network structure of anE-UMTS as an exemplary radio communication system. An Evolved UniversalMobile Telecommunications System (E-UMTS) is an advanced version of aconventional Universal Mobile Telecommunications System (UMTS) and basicstandardization thereof is currently underway in the 3GPP. E-UMTS may begenerally referred to as a Long Term Evolution (LTE) system. For detailsof the technical specifications of the UMTS and E-UMTS, reference can bemade to Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells are present per eNB. A cell is configured to use oneof bandwidths of 1.44, 3, 5, 10, 15, and 20 MHz to provide a downlink oruplink transport service to several UEs. Different cells may be set toprovide different bandwidths. The eNB controls data transmission andreception for a plurality of UEs. The eNB transmits downlink schedulinginformation with respect to downlink data to notify a corresponding UEof a time/frequency domain in which data is to be transmitted, coding,data size, and Hybrid Automatic Repeat and reQuest (HARQ)-relatedinformation. In addition, the eNB transmits uplink schedulinginformation with respect to uplink data to a corresponding UE to informthe UE of an available time/frequency domain, coding, data size, andHARQ-related information. An interface may be used to transmit usertraffic or control traffic between eNBs. A Core Network (CN) may includethe AG, a network node for user registration of the UE, and the like.The AG manages mobility of a UE on a Tracking Area (TA) basis, each TAincluding a plurality of cells.

Although radio communication technology has been developed up to LTEbased on Wideband Code Division Multiple Access (WCDMA), demands andexpectations of users and providers continue to increase. In addition,since other radio access technologies continue to be developed, newadvances in technology are required to secure future competitiveness.For example, decrease of cost per bit, increase of service availability,flexible use of a frequency band, simple structure, open interface, andsuitable power consumption by a UE are required.

DISCLOSURE OF INVENTION Technical Problem

Based on the above discussion, the present invention proposes a methodfor managing packets for a V2X (Vehicle-to-Everything) communication andan apparatus therefor.

Solution to Problem

In accordance with an embodiment of the present invention, a method fordiscarding at least one packet by a user equipment (UE) in a wirelesscommunication system is disclosed. The method includes the steps ofstoring the at least one packet received from an upper layer in abuffer; determining whether or not a number of packets in the buffer isequal to or greater than a threshold value; and discarding the at leastone packet from the buffer when the number of packets in the buffer isequal to or greater than the threshold value.

Further, in accordance with another embodiment of the present invention,a user equipment (UE) in a wireless communication system is disclosed.The UE comprises a radio frequency (RF) unit; and a processor connectedwith the RF unit and configured to store the at least one packetreceived from an upper layer in a buffer, determine whether or not anumber of packets in the buffer is equal to or greater than a threshold,and discard the at least one packet from the buffer when the number ofpackets in the buffer is equal to or greater than the threshold value.

As a special case, if the threshold value is 1, the at least one packetis discarded upon a detection of ingress of another packet into thebuffer.

Preferably, when determining whether or not the number of packets in thebuffer is equal to or greater than the threshold value or not, onlypackets having same priority may be considered. Therefore, thedetermining comprises determining whether or not a number of packetshaving same priority in the buffer is equal to or greater than thethreshold value.

Preferably, information about the threshold value may be provided fromthe network. Especially, the threshold value is configured per bearer

Furthermore, according to the present invention, it is preferable todetermine whether a zone in which the UE is located is changed or not.In this case, when the zone is changed, the at least one packet isdiscarded from the buffer.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Advantageous Effects of Invention

According to embodiments of the present invention, the UE can managepackets efficiently for the V2X communication.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present invention are notlimited to what has been particularly described hereinabove and otheradvantages of the present invention will be more clearly understood fromthe following detailed description.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 is a diagram showing a network structure of an Evolved UniversalMobile Telecommunications System (E-UMTS) as an example of a wirelesscommunication system.

FIG. 2 is a diagram showing the concept of a network structure of anEvolved Universal Terrestrial Radio Access Network (E-UTRAN).

FIG. 3 is a diagram showing a control plane and a user plane of a radiointerface protocol between a User Equipment (UE) and an EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN) based on a 3rdGeneration Partnership Project (3GPP) radio access network standard.

FIG. 4 is a diagram showing physical channels used in a 3GPP system anda general signal transmission method using the same.

FIG. 5 is a diagram showing the structure of a radio frame used in aLong Term Evolution (LTE) system.

FIG. 6 is an example of default data path for a normal communication;

FIGS. 7 and 8 are examples of data path scenarios for a proximitycommunication;

FIG. 9 is a conceptual diagram illustrating for a non-roaming referencearchitecture;

FIG. 10 is a conceptual diagram illustrating for a Layer 2 Structure forSidelink;

FIG. 11 is a conceptual diagram illustrating for protocol stack forProSe Direct Communication;

FIG. 12 is a conceptual diagram illustrating for a PC5 interface forProSe Direct Discovery;

FIG. 13 is a conceptual diagram illustrating for Vehicle-to-Everything(V2X) communication;

FIG. 14 is a flow chart illustrating an operation in accordance with anembodiment of the present invention; and

FIG. 15 is a block diagram of a communication apparatus according to anembodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, structures, operations, and other features of the presentinvention will be readily understood from the embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. Embodiments described later are examples in which technicalfeatures of the present invention are applied to a 3GPP system.

Although the embodiments of the present invention are described using along term evolution (LTE) system and a LTE-advanced (LTE-A) system inthe present specification, they are purely exemplary. Therefore, theembodiments of the present invention are applicable to any othercommunication system corresponding to the above definition. In addition,although the embodiments of the present invention are described based ona frequency division duplex (FDD) scheme in the present specification,the embodiments of the present invention may be easily modified andapplied to a half-duplex FDD (H-FDD) scheme or a time division duplex(TDD) scheme.

FIG. 2 is a diagram showing the concept of a network structure of anEvolved Universal Terrestrial Radio Access Network (E-UTRAN). Inparticular, the E-UTRAN system is a system evolved from the existingUTRAN system. The E-UTRAN includes cells (eNBs) and cells are connectedvia an X2 interface. A cell is connected to a user equipment (UE) via anair interface and is connected to an evolved packet core (EPC) via an S1interface.

The EPC includes a mobility management entity (MME), a serving-gateway(S-GW) and a packet data network-gateway (PDN-GW). The MME has accessinformation of a UE and information about capabilities of the UE. Suchinformation is mainly used for mobility management of the UE. The S-GWis a gateway having an E-UTRAN as an end point and the PDN-GW is agateway having a PDN as an end point.

FIG. 3 shows a control plane and a user plane of a radio interfaceprotocol between a UE and an Evolved Universal Terrestrial Radio AccessNetwork (E-UTRAN) based on a 3GPP radio access network standard. Thecontrol plane refers to a path used for transmitting control messagesused for managing a call between the UE and the network. The user planerefers to a path used for transmitting data generated in an applicationlayer, e.g., voice data or Internet packet data.

A physical (PHY) layer of a first layer provides an information transferservice to a higher layer using a physical channel. The PHY layer isconnected to a Medium Access Control (MAC) layer located on a higherlayer via a transport channel. Data is transported between the MAC layerand the PHY layer via the transport channel. Data is also transportedbetween a physical layer of a transmitting side and a physical layer ofa receiving side via a physical channel. The physical channel uses atime and a frequency as radio resources. More specifically, the physicalchannel is modulated using an Orthogonal Frequency Division MultipleAccess (OFDMA) scheme in downlink and is modulated using aSingle-Carrier Frequency Division Multiple Access (SC-FDMA) scheme inuplink.

A medium access control (MAC) layer, a radio link control (RLC) layerand a packet data convergence protocol (PDCP) layer may be located in asecond layer. The MAC layer of the second layer serves to map variouslogical channels to various transport channels. The MAC layer performs alogical channel multiplexing function for mapping several logicalchannels to one transport channel. The MAC layer is connected to a RadioLink Control (RLC) layer, which is a higher layer, via a logicalchannel, and the logical channel may be roughly divided into a controlchannel for transmitting information about the control plane and atraffic channel for transmitting information about the user plane,according to the type of transmitted information.

The RLC layer of the second layer segments and concatenates datareceived from a higher layer, thereby controlling a data size suitablefor enabling a lower layer to transmit data in a radio interval. The RLClayer provides three modes, namely, a transparent mode (TM), anunacknowledged mode (UM) and an acknowledged mode (AM) to support avariety of QoS requested by each radio bearer (RB). Especially, forreliable data transmission, the AM RLC performs a function to retransmitdata through automatic repeat request (ARQ).

The packet data convergence protocol (PDCP) layer of the second layerperforms a header compression function for reducing the size of an IPpacket header which is relatively great in size and includes unnecessarycontrol information in order to efficiently transmit IP packets, such asIPv4 or IPv6 packets, in a radio interval with a relatively narrowbandwidth. Accordingly, only necessary information need be included inthe header part of data for transmission, so as to increase transmissionefficiency of a radio interval. In the LTE system, the PDCP layer alsoperforms a security function. The security function includes a cipheringfunction for preventing data monitoring from a third party, and anintegrity protection function for preventing third party datamanipulation.

A radio resource control (RRC) layer of the third layer is defined onlyin the control plane. The RRC layer handles logical channels, transportchannels and physical channels for the configuration, re-configurationand release of radio bearers (RBs). Here, a radio bearer (RB) denotes aservice provided by the second layer for data transfer between the UEand the network. The RRC layers of the UE and the network exchange RRCmessages with each other.

The RB may be broadly divided into two bearers, that is, a signalingradio bearer (SRB) used to transmit an RRC message on a control planeand a data radio bearer (DRB) used to transmit user data on a userplane. The DRB may be divided into a UM DRB using UM RLC and AM DRBusing AM RLC according to method for operating RLC.

Hereinafter, an RRC state of a UE and an RRC connection method will bedescribed. The RRC state, which indicates whether the RRC layer of theUE is logically connected to the RRC layer of the E-UTRAN, is called anRRC_CONNECTED state if the RRC layers are connected and is called anRRC_IDLE state if the RRC layers are not connected.

Since the E-UTRAN detects presence of a UE in an RRC_CONNECTED state incell units, it is possible to efficiently control the UE. In contrast,the E-UTRAN cannot detect a UE in an RRC_IDLE state in cell units and acore network (CN) manages the UE in an RRC_IDLE state in units of TAwhich is greater than a cell. That is, the UE in the RRC_IDLE statetransitions to the RRC_CONNECTED state in order to receive a servicesuch as voice or data from a cell.

In particular, when a user first turns a UE on, the UE searches for anappropriate cell and then camps on an RRC_IDLE state in the cell. The UEin the RRC_IDLE state performs an RRC connection establishment processwith the RRC layer of the E-UTRAN to transition to the RRC_CONNECTEDstate when RRC connection needs to be established. The RRC connectionneeds to be established when uplink data transmission is necessary dueto call connection attempt of a user, when a response message istransmitted in response to a paging message received from the E-UTRAN,etc.

A non-access stratum (NAS) layer located above the RRC layer performs afunction such as session management and mobility management. In the NASlayer, two states such as an EPS mobility management-REGISTERED(EMM-REGISTERED) state and an EMM-UNREGISTERED state are defined inorder to manage mobility of a UE. These two states are applied to the UEand the MME. A UE is first in the EMM-UNREGISTERED state and performs aprocess of registering with a network through an initial attachprocedure in order to access the network. If the attach procedure issuccessfully performed, the UE and the MME enter the EMM-REGISTEREDSTATE.

In the NAS layer, in order to manage signaling connection between the UEand the EPC, an EPS connection management (ECM)-IDLE state and anECM_CONNECTED state are defined and applied to the UE and the MME. If aUE in the ECM-IDLE state is RRC connected to the E-UTRAN, the UE entersthe ECM-CONNECTED state. If the MME in the ECM-IDLE state is S1connected to the E-UTRAN, the MME enters the ECM-CONNECTED state.

When the UE is in the ECM-IDLE state, the E-UTRAN does not have contextinformation of the UE. Accordingly, the UE in the ECM-IDLE stateperforms a UEbased mobility associated procedure, such as cell selectionor reselection, without receiving a command of the network. In contrast,if the UE is in the ECM-CONNECTED state, mobility of the UE is managedby the command of the network. If the location of the UE is changed inthe ECM-IDLE state, the UE informs the network of the location thereofvia a tracking area (TA) update procedure.

In an LTE system, one cell configuring an eNB is configured to use abandwidth such as 1.25, 2.5, 5, 10, 15 or 20 MHz to provide a downlinkor uplink transmission service to several UEs. Different cells may beconfigured to provide different bandwidths.

Downlink transport channels for transmission of data from the network tothe UE include a Broadcast Channel (BCH) for transmission of systeminformation, a Paging Channel (PCH) for transmission of paging messages,and a downlink Shared Channel (SCH) for transmission of user traffic orcontrol messages. Traffic or control messages of a downlink multicast orbroadcast service may be transmitted through a downlink SCH and may alsobe transmitted through a downlink multicast channel (MCH).

Uplink transport channels for transmission of data from the UE to thenetwork include a Random Access Channel (RACH) for transmission ofinitial control messages and an uplink SCH for transmission of usertraffic or control messages. Logical channels, which are located abovethe transport channels and are mapped to the transport channels, includea Broadcast Control Channel (BCCH), a Paging Control Channel (PCCH), aCommon Control Channel (CCCH), a Multicast Control Channel (MCCH), and aMulticast Traffic Channel (MTCH).

FIG. 4 is a diagram showing physical channels used in a 3GPP system anda general signal transmission method using the same.

A UE performs an initial cell search operation such as synchronizationwith an eNB when power is turned on or the UE enters a new cell (S401).The UE may receive a Primary Synchronization Channel (P-SCH) and aSecondary Synchronization Channel (S-SCH) from the eNB, performsynchronization with the eNB, and acquire information such as a cell ID.Thereafter, the UE may receive a physical broadcast channel from the eNBso as to acquire broadcast information within the cell. Meanwhile, theUE may receive a Downlink Reference Signal (DL RS) so as to confirm adownlink channel state in the initial cell search step.

The UE which has completed the initial cell search may receive aPhysical Downlink Control Channel (PDCCH) and a Physical Downlink SharedChannel (PDSCH) according to information included in the PDCCH so as toacquire more detailed system information (S402).

Meanwhile, if the eNB is initially accessed or radio resources forsignal transmission are not present, the UE may perform a Random AccessProcedure (RACH) (step S403 to S406) with respect to the eNB. In thiscase, the UE may transmit a specific sequence through a Physical RandomAccess Channel (PRACH) as a preamble (S403), and receive a responsemessage to the preamble through the PDCCH and the PDSCH correspondingthereto (S404). In case of contention based RACH, a contentionresolution procedure may be further performed.

The UE which has performed the above procedures may perform PDCCH/PDSCHreception (S407) and Physical Uplink Shared Channel PUSCH)/PhysicalUplink Control Channel (PUCCH) transmission (S408) as a generaluplink/downlink signal transmission procedure. In particular, the UEreceives downlink control information (DCI) via a PDCCH. The DCIincludes control information such as resource allocation information ofthe UE and the format thereof is changed according to use purpose.

The control information transmitted from the UE to the eNB in uplink ortransmitted from the eNB to the UE in downlink includes adownlink/uplink ACK/NACK signal, a Channel Quality Indicator (CQI), aPrecoding Matrix Index (PMI), a Rank Indicator (RI), and the like. Incase of the 3GPP LTE system, the UE may transmit the control informationsuch as CQI/PMI/RI through the PUSCH and/or the PUCCH.

FIG. 5 is a diagram showing the structure of a radio frame used in aLong Term Evolution (LTE) system.

Referring to FIG. 5, the radio frame has a length of 10 ms(327200×T_(s)) and includes 10 subframes with the same size. Eachsubframe has a length of 1 ms and includes two slots. Each slot has alength of 0.5 ms (15360×T_(s)). T_(s) denotes a sampling time, and isrepresented by T_(s)=1/(15 kHz×2048)=3.2552×10⁻⁸ (about 33 ns). Eachslot includes a plurality of OFDM symbols in a time domain, and includesa plurality of resource blocks (RBs) in a frequency domain. In the LTEsystem, one RB includes 12 sub-carriers×7(6) OFDM or SC-FDMA symbols. ATransmission Time Interval (TTI) which is a unit time for transmissionof data may be determined in units of one or more subframes. Thestructure of the radio frame is only exemplary and the number ofsubframes included in the radio frame, the number of slots included inthe subframe, or the number of OFDM symbols included in the slot may bevariously changed.

Recently, Proximity-based Service (ProSe) has been discussed in 3GPP.The ProSe enables different UEs to be connected (directly) each other(after appropriate procedure(s), such as authentication), through eNBonly (but not further through Serving Gateway (SGW)/Packet Data NetworkGateway (PDN-GW, PGW)), or through SGW/PGW. Thus, using the ProSe,device to device direct communication can be provided, and it isexpected that every devices will be connected with ubiquitousconnectivity. Direct communication between devices in a near distancecan lessen the load of network. Recently, proximity-based social networkservices have come to public attention, and new kinds of proximity-basedapplications can be emerged and may create new business market andrevenue. For the first step, public safety and critical communicationare required in the market. Group communication is also one of keycomponents in the public safety system. Required functionalities are:Discovery based on proximity, Direct path communication, and Managementof group communications.

Use cases and scenarios are for example: i) Commercial/social use, ii)Network offloading, iii) Public Safety, iv) Integration of currentinfrastructure services, to assure the consistency of the userexperience including reachability and mobility aspects, and v) PublicSafety, in case of absence of EUTRAN coverage (subject to regionalregulation and operator policy, and limited to specific public-safetydesignated frequency bands and terminals)

FIG. 6 is an example of default data path for communication between twoUEs. With reference to FIG. 6, even when two UEs (e.g., UE1, UE2) inclose proximity communicate with each other, their data path (userplane) goes via the operator network. Thus a typical data path for thecommunication involves eNB(s) and/or Gateway(s) (GW(s)) (e.g., SGW/PGW).

FIGS. 7 and 8 are examples of data path scenarios for a proximitycommunication. If wireless devices (e.g., UE1, UE2) are in proximity ofeach other, they may be able to use a direct mode data path (FIG. 7) ora locally routed data path (FIG. 8). In the direct mode data path,wireless devices are connected directly each other (after appropriateprocedure(s), such as authentication), without eNB and SGW/PGW. In thelocally routed data path, wireless devices are connected each otherthrough eNB only.

FIG. 9 is a conceptual diagram illustrating for a non-roaming referencearchitecture.

PC1 to PC 5 represent interfaces. PC1 is a reference point between aProSe application in a UE and a ProSe App server. It is used to defineapplication level signaling requirements. PC 2 is a reference pointbetween the ProSe App Server and the ProSe Function. It is used todefine the interaction between ProSe App Server and ProSe functionalityprovided by the 3GPP EPS via ProSe Function. One example may be forapplication data updates for a ProSe database in the ProSe Function.Another example may be data for use by ProSe App Server in interworkingbetween 3GPP functionality and application data, e.g. name translation.PC3 is a reference point between the UE and ProSe Function. It is usedto define the interaction between UE and ProSe Function. An example maybe to use for configuration for ProSe discovery and communication. PC4is a reference point between the EPC and ProSe Function. It is used todefine the interaction between EPC and ProSe Function. Possible usecases may be when setting up a one-to-one communication path between UEsor when validating ProSe services (authorization) for session managementor mobility management in real time.

PC5 is a reference point between UE to UE used for control and userplane for discovery and communication, for relay and one-to-onecommunication (between UEs directly and between UEs over LTE-Uu).Lastly, PC6 is a reference point may be used for functions such as ProSeDiscovery between users subscribed to different PLMNs.

EPC (Evolved Packet Core) includes entities such as MME, S-GW, P-GW,PCRF, HSS etc. The EPC here represents the E-UTRAN Core Networkarchitecture. Interfaces inside the EPC may also be impacted albeit theyare not explicitly shown in FIG. 9.

Application servers, which are users of the ProSe capability forbuilding the application functionality, e.g. in the Public Safety casesthey can be specific agencies (PSAP) or in the commercial cases socialmedia. These applications are defined outside the 3GPP architecture butthere may be reference points towards 3GPP entities. The Applicationserver can communicate towards an application in the UE.

Applications in the UE use the ProSe capability for building theapplication functionality. Example may be for communication betweenmembers of Public Safety groups or for social media application thatrequests to find buddies in proximity. The ProSe Function in the network(as part of EPS) defined by 3GPP has a reference point towards the ProSeApp Server, towards the EPC and the UE.

The functionality may include but not restricted to e.g.:

-   -   Interworking via a reference point towards the 3rd party        Applications    -   Authorization and configuration of the UE for discovery and        Direct communication    -   Enable the functionality of the EPC level ProSe discovery    -   ProSe related new subscriber data and/handling of data storage;        also handling of ProSe identities;    -   Security related functionality    -   Provide Control towards the EPC for policy related functionality    -   Provide functionality for charging (via or outside of EPC, e.g.        offline charging)

Especially, the following identities are used for ProSe DirectCommunication:

-   -   Source Layer-2 ID identifies a sender of a D2D packet at PC5        interface. The Source Layer-2 ID is used for identification of        the receiver RLC UM entity;    -   Destination Layer-2 ID identifies a target of the D2D packet at        PC5 interface. The Destination Layer-2 ID is used for filtering        of packets at the MAC layer. The Destination Layer-2 ID may be a        broadcast, groupcast or unicast identifier; and    -   SA L1 ID identifier in Scheduling Assignment (SA) at PC5        interface. SA L1 ID is used for filtering of packets at the        physical layer. The SA L1 ID may be a broadcast, groupcast or        unicast identifier.

No Access Stratum signaling is required for group formation and toconfigure Source Layer-2 ID and Destination Layer-2 ID in the UE. Thisinformation is provided by higher layers.

In case of groupcast and unicast, the MAC layer will convert the higherlayer ProSe ID (i.e. ProSe Layer-2 Group ID and ProSe UE ID) identifyingthe target (Group, UE) into two bit strings of which one can beforwarded to the physical layer and used as SA L1 ID whereas the otheris used as Destination Layer-2 ID. For broadcast, L2 indicates to L1that it is a broadcast transmission using a pre-defined SA L1 ID in thesame format as for group- and unicast.

FIG. 10 is a conceptual diagram illustrating for a Layer 2 structure forSidelink

The Sidelink is UE to UE interface for ProSe direct communication andProSe Direct Discovery. Corresponds to the PC5 interface. The Sidelinkcomprises ProSe Direct Discovery and ProSe Direct Communication betweenUEs. The Sidelink uses uplink resources and physical channel structuresimilar to uplink transmissions. However, some changes, noted below, aremade to the physical channels. E-UTRA defines two MAC entities; one inthe UE and one in the E-UTRAN. These MAC entities handle the followingtransport channels additionally, i) sidelink broadcast channel (SL-BCH),ii) sidelink discovery channel (SL-DCH) and iii) sidelink shared channel(SL-SCH).

-   -   Basic transmission scheme: the Sidelink transmission uses the        same basic transmission scheme as the UL transmission scheme.        However, sidelink is limited to single cluster transmissions for        all the sidelink physical channels. Further, sidelink uses a 1        symbol gap at the end of each sidelink sub-frame.    -   Physical-layer processing: the Sidelink physical layer        processing of transport channels differs from UL transmission in        the following steps:

i) Scrambling: for PSDCH and PSCCH, the scrambling is not UE-specific;

ii) Modulation: 64 QAM is not supported for Sidelink

-   -   Physical Sidelink control channel: PSCCH is mapped to the        Sidelink control resources. PSCCH indicates resource and other        transmission parameters used by a UE for PSSCH.    -   Sidelink reference signals: for PSDCH, PSCCH and PSSCH        demodulation, reference signals similar to uplink demodulation        reference signals are transmitted in the 4th symbol of the slot        in normal CP and in the 3rd symbol of the slot in extended        cyclic prefix. The Sidelink demodulation reference signals        sequence length equals the size (number of sub-carriers) of the        assigned resource. For PSDCH and PSCCH, reference signals are        created based on a fixed base sequence, cyclic shift and        orthogonal cover code.    -   Physical channel procedure: for in-coverage operation, the power        spectral density of the sidelink transmissions can be influenced        by the eNB.

FIG. 11 is a conceptual diagram illustrating for protocol stack forProSe Direct Communication.

FIG. 11(a) shows the protocol stack for the user plane, where PDCP, RLCand MAC sublayers (terminate at the other UE) perform the functionslisted for the user plane (e.g. header compression, HARQretransmissions). The PC5 interface consists of PDCP, RLC, MAC and PHYas shown in FIG. 11 a.

User plane details of ProSe Direct Communication: i) MAC sub headercontains LCIDs (to differentiate multiple logical channels), ii) The MACheader comprises a Source Layer-2 ID and a Destination Layer-2 ID, iii)At MAC Multiplexing/demultiplexing, priority handling and padding areuseful for ProSe Direct communication, iv) RLC UM is used for ProSeDirect communication, v) Segmentation and reassembly of RLC SDUs areperformed, vi) A receiving UE needs to maintain at least one RLC UMentity per transmitting peer UE, vii) An RLC UM receiver entity does notneed to be configured prior to reception of the first RLC UM data unit,and viii) U-Mode is used for header compression in PDCP for ProSe DirectCommunication.

FIG. 11(b) shows the protocol stack for the control plane, where RRC,RLC, MAC, and PHY sublayers (terminate at the other UE) perform thefunctions listed for the control plane. A D2D UE does not establish andmaintain a logical connection to receiving D2D UEs prior to a D2Dcommunication.

FIG. 12 is a conceptual diagram illustrating for a PC5 interface forProSe Direct Discovery.

ProSe Direct Discovery is defined as the procedure used by theProSe-enabled UE to discover other ProSe-enabled UE(s) in its proximityusing E-UTRA direct radio signals via PC5.

Radio Protocol Stack (AS) for ProSe Direct Discovery is shown in FIG.12.

The AS layer performs the following functions:

-   -   Interfaces with upper layer (ProSe Protocol): The MAC layer        receives the discovery information from the upper layer (ProSe        Protocol). The IP layer is not used for transmitting the        discovery information.    -   Scheduling: The MAC layer determines the radio resource to be        used for announcing the discovery information received from        upper layer.    -   Discovery PDU generation: The MAC layer builds the MAC PDU        carrying the discovery information and sends the MAC PDU to the        physical layer for transmission in the determined radio        resource. No MAC header is added.

There are two types of resource allocation for discovery informationannouncement.

-   -   Type 1: A resource allocation procedure where resources for        announcing of discovery information are allocated on a non UE        specific basis, further characterized by: i) The eNB provides        the UE(s) with the resource pool configuration used for        announcing of discovery information. The configuration may be        signalled in SIB, ii) The UE autonomously selects radio        resource(s) from the indicated resource pool and announce        discovery information, iii) The UE can announce discovery        information on a randomly selected discovery resource during        each discovery period.    -   Type 2: A resource allocation procedure where resources for        announcing of discovery information are allocated on a per UE        specific basis, further characterized by: i) The UE in        RRC_CONNECTED may request resource(s) for announcing of        discovery information from the eNB via RRC, ii) The eNB assigns        resource(s) via RRC, iii) The resources are allocated within the        resource pool that is configured in UEs for monitoring.

For UEs in RRC_IDLE, the eNB may select one of the following options:

-   -   The eNB may provide a Type 1 resource pool for discovery        information announcement in SIB. UEs that are authorized for        Prose Direct Discovery use these resources for announcing        discovery information in RRC_IDLE.    -   The eNB may indicate in SIB that it supports D2D but does not        provide resources for discovery information announcement. UEs        need to enter RRC Connected in order to request D2D resources        for discovery information announcement.

For UEs in RRC_CONNECTED,

-   -   A UE authorized to perform ProSe Direct Discovery announcement        indicates to the eNB that it wants to perform D2D discovery        announcement.    -   The eNB validates whether the UE is authorized for ProSe Direct        Discovery announcement using the UE context received from MME.    -   The eNB may configure the UE to use a Type 1 resource pool or        dedicated Type 2 resources for discovery information        announcement via dedicated RRC signaling (or no resource).    -   The resources allocated by the eNB are valid until a) the eNB        de-configures the resource(s) by RRC signaling or b) the UE        enters IDLE. (FFS whether resources may remain valid even in        IDLE).

Receiving UEs in RRC_IDLE and RRC_CONNECTED monitor both Type 1 and Type2 discovery resource pools as authorized. The eNB provides the resourcepool configuration used for discovery information monitoring in SIB. TheSIB may contain discovery resources used for announcing in neighborcells as well.

FIG. 13 is a conceptual diagram illustrating for Vehicle-to-Everything(V2X) communication;

Referring to FIG. 13, the vehicular communication, referred to asVehicleto-Everything (V2X), can be divided into three different typesincluding Vehicleto-Vehicle (V2V) Communications,Vehicle-to-Infrastructure (V2I) Communications and Vehicle-to-Pedestrian(V2P) Communications.

These three types of V2X can use “co-operative awareness” to providemore intelligent services for end-users. This means that transportentities, such as vehicles, roadside infrastructure, and pedestrians,can collect knowledge of their local environment (e.g., informationreceived from other vehicles or sensor equipment in proximity) toprocess and share that knowledge in order to provide more intelligentservices, such as cooperative collision warning or autonomous driving.

Vehicle-to-Vehicle (V2V)

E-UTRAN allows such UEs that are in proximity of each other to exchangeV2V-related information using E-UTRA(N) when permission, authorizationand proximity criteria are fulfilled. The proximity criteria can beconfigured by the MNO. However, UEs supporting V2V Service can exchangesuch information when served by or not served by E-UTRAN which supportsV2X Service.

The UE supporting V2V applications transmits application layerinformation (e.g. about its location, dynamics, and attributes as partof the V2V Service). The V2V payload must be flexible in order toaccommodate different information contents, and the information can betransmitted periodically according to a configuration provided by theMNO.

V2V is predominantly broadcast-based; V2V includes the exchange ofV2V-related application information between distinct UEs directlyand/or, due to the limited direct communication range of V2V, theexchange of V2V-related application information between distinct UEs viainfrastructure supporting V2X Service, e.g., RSU (road side unit),application server, etc.

Vehicle-to-Infrastructure (V2I)

The UE supporting V2I applications sends application layer informationto RSU. RSU sends application layer information to a group of UEs or aUE supporting V2I applications.

V2N is also introduced where one party is a UE and the other party is aserving entity, both supporting V2N applications and communicating witheach other via LTE network.

Vehicle-to-Pedestrian (V2P)

E-UTRAN allows such UEs that are in proximity of each other to exchangeV2P-related information using E-UTRAN when permission, authorization andproximity criteria are fulfilled. The proximity criteria can beconfigured by the MNO. However, UEs supporting V2P Service can exchangesuch information even when not served by E-UTRAN which supports V2XService.

The UE supporting V2P applications transmits application layerinformation. Such information can be broadcast by a vehicle with UEsupporting V2X Service (e.g., warning to pedestrian), and/or by apedestrian with UE supporting V2X Service (e.g., warning to vehicle).

V2P includes the exchange of V2P-related application information betweendistinct UEs (one for vehicle and the other for pedestrian) directlyand/or, due to the limited direct communication range of V2P, theexchange of V2P-related application information between distinct UEs viainfrastructure supporting V2X Service, e.g., RSU, application server,etc.

Hereinafter, a discard procedure of a PDCP (packet data convergenceprotocol) SDU (service data unit) will be described.

At reception of a PDCP SDU from upper layers, the UE shall start adiscardTimer associated with this PDCP SDU. Then, when the discardTimerexpires for a PDCP SDU, or the successful delivery of a PDCP SDU isconfirmed by PDCP status report, the UE shall discard the PDCP SDU alongwith the corresponding PDCP PDU. If the corresponding PDCP PDU hasalready been submitted to lower layers the discard is indicated to lowerlayers.

The discardTimer is configured by upper layers. In the transmitter, anew timer is started upon reception of an SDU from upper layer. Thereceiving side of each PDCP entity shall maintain the following timersonly when the reordering function is used.

Hereinafter, it is described how the mechanism L2 layer (e.g. PDCPlayer) discards the packets in the buffer. In the following, theinvention describes about the PDCP layer behavior, however, the scope ofthe invention is not limited to PDCP layer.

First Embodiment

In the First Embodiment of the present invention, the PDCP layerdiscards the PDCP

SDU(s) which is already in PDCP buffer even if the PDCP discard timer isstill running upon detection of:

-   -   the number of SDUs in PDCP buffer for an indicated bearer is        more than (or equal to) a threshold; and/or    -   The number of SDUs of the same priority/QoS/QCI value in PDCP        buffer is more than (or equal to) a threshold. Here, it is        assumed that PDCP SDUs having different prioritis exist in one        bearer.

Especially, the threshold value can be configured or fixed. Or, thethreshold value can be configured per destination. Then, PDCP entitycounts the number of SDUs in the buffer as per destination and comparesthe threshold value associated with the destination. Further, the numberSDUs in the buffer may include RLC SDUs if no segment of the RLC SDU hasbeen mapped to a RLC data PDU yet.

As a baseline, at reception of a PDCP SDU from upper layers, the UEshall start the PDCP discard timer called as discardTimer associatedwith this PDCP SDU. The assumption is that upper layer provides thepriority/QoS/QCI information to lower layer (e.g PDCP entity) with SDU.

The priority described above is a priority of a packet (e.g. PPPP (ProSePer-Packet Priority), other priority considering priority, latency andloss rate). The QoS information can be defined by e.g. priority, latencyrequirement and/or loss rate. The QoS information is classified intolevels. The level has an associated priority, latency requirement and/orloss rate.

For the above behavior, the network configures/indicates whether thePDCP entity of the UE shall perform above behavior when the network setup a radio bearer or modifies a radio bearer configuration. If PDCPentity of the UE is allowed to perform discard behavior of theinvention, the PDCP entity shall perform as described above. Otherwise,the PDCP entity behaves as legacy.

The configuration information includes:

-   -   Indication on whether PDCP entity of the UE shall perform        discard behavior described above,    -   Priority/QoS/QCI information which needs to be handled by this        invention,    -   The threshold number of up-to-date SDU(s) to be stored (or to be        transmitted) in PDCP buffer per PDCP entity,    -   The threshold number of up-to-date SDU(s) to be stored (or to be        transmitted) in PDCP buffer per destination and per PDCP entity.

A special case of the above invention is that only one (up-to-date) PDCPSDU is allowed to be stored and transmitted. In this case, the PDCPlayer discards the PDCP SDU(s) which is already in PDCP buffer even ifthe PDCP discard timer is still running upon detection of an ingress ofother SDUs of a same priority/QoS/QCI in PDCP buffer and/or an ingressof other SDUs into the indicated bearer.

Consequently, according to the First Embodiment of the presentapplication, it is suggested to enhance the discard procedure of a PDCPSDU. Specifically, when the discardTimer expires for a PDCP SDU, thesuccessful delivery of a PDCP SDU is confirmed by PDCP status report, oringress of another SDU(s) of the same QoS level if indicated by upperlayer, the UE shall discard the PDCP SDU along with the correspondingPDCP PDU. If the corresponding PDCP PDU has already been submitted tolower layers the discard is indicated to lower layers.

Second Embodiment

Even before a discard timer associated with a particular PDCP SDUexpires, it seems to be necessary to discard the SDU since theinformation in SDU is not valid any more.

In the Second Embodiment of the present application, it is proposed ofthe method of discarding the transmitted SDUs/PDUs which is nottransmitted yet and is in the L2 buffer. Especially, the proposeddiscarding method comprises steps 1) and 2) following.

Step 1)

Firstly, the UE detects at least one of the following events A)-E).

A) The reference position changes

It is assumed that multiple reference positions are provided viabroadcast/dedicated signaling. The UE selects the closet referencepositions among the provided multiple reference positions.

B) The zone changes

Zone can be defined in various ways. The examples of zones are as shownbelow (a)-(c):

(a) A zone may be defined by multiple coordinates (e.g. four coordinatesX, Y, Z, W). The coordinates are presented by latitude and longitude.The UE detects the zone to which it belongs by the position of the UE.If the UE's current position is in the certain area represented by themultiple coordinates, the UE determines that it is in the zone.

(b) A zone may be defined with one reference position and length/width.The reference position is indicated by latitude and longitude. The UEdetects the zone to which it belongs by the position of the UE. If theUE's current position is in the certain area represented by the multiplecoordinates, the UE determines that it is in the zone.

(c) A zone may be defined by multiple reference positions. Eachreference position is represented by latitude and longitude. The UEselects the closet reference positions and determines that it belongs tothe area of the reference position.

C) The current position of the UE becomes far from the last reportedposition by a threshold value.

D) The current speed of the UE becomes higher/less than the lastreported speed by a threshold value.

E) The heading (or direction) of the UE becomes different from the lastreported heading by a threshold value.

Especially, the current position/speed/heading of the UE can bedetermined within one zone or can be determined by using the number ofzones through which the UE moves.

Further, the threshold value for position/speed/heading is given by thededicated/broadcast signaling. The layer of the UE which detects theevents can be RRC.

Step 2)

When the UE detects one of the above events, the UE (e.g. RRC layer ofthe UE) indicates to L2 entity that SDU/PDUs that are not transmittedyet are discarded. Then, the PDCP layer discards the PDCP SDU(s) whichis already in PDCP buffer even if the PDCP discard timer is stillrunning. The PDCP layer also indicates the RLC layer to discardunnecessary RLC SDUs in the bearer associated with the PDCP entity. Whenindicated from upper layer (i.e. PDCP) to discard a particular RLC SDU,the transmitting side of an AM RLC entity or the transmitting UM RLCentity shall discard the indicated RLC SDU if no segment of the RLC SDUhas been mapped to a RLC data PDU yet.

FIG. 14 is a flow chart illustrating an operation in accordance with anembodiment of the present invention.

Referring to FIG. 14, in S1401, a specific layer entity (for example,PDCP layer entity) of the UE may receive a packet from an upper layerand store the packet in a buffer (i.e., PDCP buffer), in S1401.Preferably, the specific layer entity starts a discard timer uponreceiving the packet received from the upper layer.

Next, in S1403, the specific layer entity may determine whether or not anumber of packets in the buffer is equal to or greater than a thresholdvalue. Here, the threshold value may be configured by a network.Preferably, the specific layer entity may consider only packets havingsame priority. In this case, the specific layer entity may determinewhether or not a number of packets having same priority in the buffer isequal to or greater than the threshold value.

Finally, in S1405, if the number of packets (having the same priority)in the buffer is equal to or greater than the threshold value, or if thediscard timer is expired, or if the packet is delivered successfully toa lower layer, the specific layer entity should discard the packet. Ifthe threshold value is 1, the packet may be discarded upon a detectionof ingress of another packet into the buffer.

Additionally, the specific layer entity may determine whether a zone inwhich the UE is located is changed or not. In this case, when the zoneis changed, the packet may be discarded in spite of other conditionssuch as the number of packets in the buffer or the discard timer.

FIG. 15 is a block diagram illustrating a communication apparatus inaccordance with an embodiment of the present invention.

Referring to FIG. 15, a communication device 1500 includes a processor1510, a memory 1520, a Radio Frequency (RF) module 1530, a displaymodule 1540, and a user interface module 1550.

The communication device 1500 is illustrated for convenience of thedescription and some modules may be omitted. Moreover, the communicationdevice 1500 may further include necessary modules. Some modules of thecommunication device 1500 may be further divided into sub-modules. Theprocessor 1510 is configured to perform operations according to theembodiments of the present invention exemplarily described withreference to the figures. Specifically, for the detailed operations ofthe processor 1510, reference may be made to the contents described withreference to FIGS. 1 to 14.

The memory 1520 is connected to the processor 1510 and stores operatingsystems, applications, program code, data, and the like. The RF module1530 is connected to the processor 1510 and performs a function ofconverting a baseband signal into a radio signal or converting a radiosignal into a baseband signal. For this, the RF module 1530 performsanalog conversion, amplification, filtering, and frequency upconversionor inverse processes thereof. The display module 1540 is connected tothe processor 1510 and displays various types of information. Thedisplay module 1540 may include, but is not limited to, a well-knownelement such as a Liquid Crystal Display (LCD), a Light Emitting Diode(LED), or an Organic Light Emitting Diode (OLED). The user interfacemodule 1550 is connected to the processor 1510 and may include acombination of well-known user interfaces such as a keypad and atouchscreen.

The above-described embodiments are combinations of elements andfeatures of the present invention in a predetermined manner. Each of theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. In the appendedclaims, it will be apparent that claims that are not explicitlydependent on each other can be combined to provide an embodiment or newclaims can be added through amendment after the application is filed.

The embodiments according to the present invention can be implemented byvarious means, for example, hardware, firmware, software, orcombinations thereof. In the case of a hardware configuration, theembodiments of the present invention may be implemented by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In the case of a firmware or software configuration, the methodaccording to the embodiments of the present invention may be implementedby a type of a module, a procedure, or a function, which performsfunctions or operations described above. For example, software code maybe stored in a memory unit and then may be executed by a processor. Thememory unit may be located inside or outside the processor to transmitand receive data to and from the processor through various well-knownmeans.

The present invention may be carried out in other specific ways thanthose set forth herein without departing from the spirit and essentialcharacteristics of the present invention. The above embodiments aretherefore to be construed in all aspects as illustrative and notrestrictive. The scope of the invention should be determined by theappended claims and their legal equivalents and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein.

INDUSTRIAL APPLICABILITY

While the above-described method for managing packets for a V2X(Vehicle-to-Everything) communication has been described centering on anexample applied to the 3GPP LTE system, the present invention isapplicable to a variety of wireless communication systems in addition tothe 3GPP LTE system.

1. A method for discarding at least one packet by a user equipment (UE)in a wireless communication system, the method comprising: storing theat least one packet received from an upper layer in a buffer;determining whether or not a number of packets in the buffer is equal toor greater than a threshold value; and discarding the at least onepacket from the buffer when the number of packets in the buffer is equalto or greater than the threshold value.
 2. The method of claim 1,wherein determining comprises determining whether or not a number ofpackets having same priority in the buffer is equal to or greater thanthe threshold value.
 3. The method of claim 1, further comprisingreceiving information about the threshold value from a network, whereinthe threshold value is configured per bearer.
 4. The method of claim 1,further comprising: starting a discard timer upon receiving the at leastone packet received from the upper layer; and discarding the at leastone packet from the buffer when the discard timer is expired or the atleast one packet is delivered successfully to a lower layer.
 5. Themethod of claim 1, wherein, if the threshold value is 1, the at leastone packet is discarded upon a detection of ingress of another packetinto the buffer.
 6. The method of claim 1, further comprising:determining whether a zone in which the UE is located is changed or not;and discarding the at least one packet from the buffer when the zone ischanged.
 7. A user equipment (UE) in a wireless communication system,the UE comprising: a radio frequency (RF) unit; and a processorconnected with the RF unit and configured to store the at least onepacket received from an upper layer in a buffer, determine whether ornot a number of packets in the buffer is equal to or greater than athreshold value, and discard the at least one packet from the bufferwhen the number of packets in the buffer is equal to or greater than thethreshold value.
 8. The UE of claim 7, wherein the processor isconfigured to determine whether or not a number of packets having samepriority in the buffer is equal to or greater than the threshold value.9. The UE of claim 7, wherein information about the threshold value isreceived from a network, wherein the threshold value is configured perbearer.
 10. The UE of claim 7, wherein the processor is furtherconfigured to start a discard timer upon receiving the at least onepacket received from the upper layer, and discard the at least onepacket from the buffer when the discard timer is expired or the at leastone packet is delivered successfully to a lower layer.
 11. The UE ofclaim 7, wherein if the threshold value is 1, the at least one packet isdiscarded upon a detection of ingress of another packet into the buffer.12. The UE of claim 7, wherein the processor is configured to determinewhether a zone in which the UE is located is changed or not, and discardthe at least one packet from the buffer when the zone is changed.